Alloy steel



Patented Oct. 8, 1929 UNITED STATES PATENT OFFICE FREDERICK F. MCINTOSH, OF GLEN OSBORNE, PENNSYLVANIA, ASSIGNOR T0 CRUCIBLE STEEL COMPANY 01 AMERICA, A CORPORATION OF NEW JERSEY ALLOY STEEL No Drawing.

This invention has to do with the class of steel now generally called stainless steel, and including the lower-carbon variety which has the arbitrar trade-name of stainless iron. It is a well nown fact that the ditliculty of machining all of the standard grades of this class of steel has prohibited its use for many industrial purposes. As the result of an extended experimental investigation I have found that by increasing the percentage of some of the elements necessarily present in the steel, but heretofore considered undesirable and therefore kept below definite maximum limits, a stainless steel can be produced which is, relatively speaking, freely machinable, while at the same time it retains, for practical purposes, its distinguishing property of surface stability.

Stainless steel is primarily distinguished in composition by its high percentage of chromium content, not less than eight per cent, and it may contain minor percentages of other alloying elements. Its carbon content should not exceed one per cent. See

' United States Letters Patent No. 1,197,256

and No. 1,299,404. Commercial products now on the market range in carbon content from about 0.10 per cent to 0.50 per cent and in chromium from about eleven per cent to eighteen per cent, or even more. Small percentages of manganese, not more than 0.50 per cent, are usually present, while the unavoidable contents of sulphur and phosphorus are strictly limited to not more than 0.03 per cent of each. As above stated, steel within the above composition ranges 1s difficult to machine. 'For example, in rifiing a .30 caliber gun-barrel made of the most suitable commercial grade of stainless steel it has been possible to turn out only about one barrel per hour with about thirty grinds on the tool.

I have discovered that by materially increasing the contents of manganese, sulphur and phorphorus, respectively, in the standard grades of stainless steel, a steel willbe obtained which is, comparatively speaking, freely machinable. For example, in rlfling .30 caliber gun-barrels made of my improved stinless steel more than two barrels per hour Application filed January 12, 1928. Serial No. 246,884.

have been turned out, with only one grind on the tool per barrel.

0 In the lower ranges of carbon content m lmproved stainless steel contains, approxlmately, carbon, 0.10-0.20 per cent, manganese, 0.901.30 per cent, phosphorus, 0.08-0.15 per cent, sulphur, 0.050.15 per cent, silicon, 0.25-0.50 per cent, and chromium, 11-15 per cent. A very desirable composition within the above limits is, carbon, 0.15 per cent, manganese, 1.02 per cent, phosphorus 0.093 per cent, sulphur, 0.107 per cent, silicon, 0.38 per cent, and chromium, 12.21 per cent. This steel was quenched in oil from 1850 F. and drawn back to 1125 F. Its Brinell hardness then was 286, its tensile strength was 120,150 pounds per square inch, its yield point was 112,050 pounds, its elongation in two nches was 19.5 per cent, and its reductlon in area 52 per cent. The same steel was subjected to carefully standardized drilling tests in comparison with several commercial grades of so-called stainless iron (carbon, .10.12, chromium, 11-14;). Under the same standard conditions the stainless iron could be drilled only about 2 inches, while the drilling of my improved stainless averaged 7. 14 inches.

In order to give the best machinable quali-- ties it is recommended that the steel shall be hardened and tempered to give it a Brinell hardness of from 265 to 290, although for partlcular purposes it can be made either softer or harder.

I use the term stainless steel in the sense that it has come to be used in the art of ferrometallurgy, as denoting a typeof alloy steel, usually within the field defined in the two Letters Patent above mentioned (either or both), although in some case a particular product may in one respect or another lie somewhat outside that field and still possess the same essential qualities. It is also well recognized that all grades and specific compositions of stainless steel will not be equally resistant to surface deterioration by the same agencies or under the same conditions; on the other hand, one composition or grade will be the better suited for one purpose and another for another. Therefore I use the term as covering a class of steel having lugh surface stability, and having carbon anol chromium contents within the limits first above set forth and as more generally stated in the said two Letters Patent, anrl especially in the Letters Patent No. 1,290,404.

I claim as my invention:

1. Alloy steel containin from about 0.10 to about 1 per cent of can on, from about 8 per cent to about 18 per cent of chromium, from about 0.9 per cent to about 1.3 per cent at manganese, from about 0.08 per cent to about 0.15 per cent of phosphorus, and from about 0.05 per cent to about 0.15 per cent of sulphur.

2. Alloy steel containing from about 0.10 per cent to about 0.20 per cent of carbon, from about 11 per cent to about 15 per cent of chromium, from about 0.9 or cent to about 1.3 per cent of manganese, rom about 0.08 per cent to about 0.15 percent of phosphorus and from about 0.05 per cent to about 0.15 per cent of sulphur.

In testimony whereof l have bereunto set my band.

FBEDERMJK l MolNTGSH. 

